1. Field of the Invention
The present invention relates to an image formation system, particularly relates to an image formation system for obtaining image information by analyzing an image formation instruction represented by language for describing an image and executing it by a plurality of image formation processors.
2. Description of the Related Art
A printing control system using "page description language" which is different from the conventional printing system mainly treating of character information and treats of an image, a graphic form and a character similarly and in which the enlargement, turning and transformation of a character and a graphic form can be freely controlled has been generally popular with the development of a printer which is suitable for high-speed digital printing such as an electrophotographic system and an ink jet system. A variety of page description languages were developed in 1980s, the representative examples are PostScript (trademark of Adobe Systems) and Interpress (trademark of Xerox) and a large number of page description languages are used for a variety of printers.
A server-type page description language processing printer shared by many users must accept a print request from many host systems, interpret print information described by page description language and execute corresponding printing. If such a printer is simultaneously utilized from many host systems, print information described by page description language is serially interpreted and executed in the printer and queuing time from a print request to the acquisition of the result has a tendency to be extended. This situation has been more serious with the enhancement of printing resolution.
To form an image in a high speed, technique for interpreting and executing an image formation instruction in parallel is proposed. For example, according to technique disclosed in PCT/JP91/00456, image formation processing on a print screen is shared by a plurality of computers distributed in a network. In this case, operation for forming an image is executed in parallel as a plurality of processes by dividing a screen as an area in which an image is formed by each computer in the shape of a band or a mesh.
According to technique disclosed in Japanese Unexamined Patent Publication No. Hei 7-104987 (1995), an image operation procedure in a document printing program is analyzed and a parallel execution code for judging whether an image can be formed in parallel or not is generated by directly comparing a pixel where an image is already formed and a pixel where an image is to be formed by the execution of the next instruction.
In the above-described conventional parallel image formation system, the judgment of overlap is required whether image formation in a portion interferes with that in another portion or not, that is, whether an image by another image formation is overwritten by an image which is to be under the above image depending upon the order of image formation or whether on the contrary, an image which is to be on an image by another image formation is overwritten by the image by another image formation or not. Particularly, the judgment of overlap is essential to graphics because graphics such as a chart is based upon the overlap of picture elements. However, as overlap between any picture element constituting a screen is required to be judged, processing time in proportion to the square of the number of picture elements is required. Therefore, there is a problem that when a picture element is divided into a few hundred or more particles, an overhead required for preprocessing for the judgment of overlap is very long and the effect of high-speed processing which is the proper object of parallel processing is greatly deteriorated.